1. Field of the Invention
The present invention relates to an automatic focusing device, and more particularly to an automatic focusing device for a digital camera.
2. Discussion of the Background
An automatic focusing device for a digital camera is known, in which a high frequency component of an image signal, which is obtained by an imaging device, such as a charged coupled device (CCD), is passed through a high band pass filter (HPF) or band pass filter (BPF). Digital values according to the intensity of the image signals passed through the HPF or BPF are integrated so as to generate a focus evaluation value for each predetermined period of time (e.g., for one field). Then, the distance between a focusing lens and the imaging device is controlled such that the focus evaluation value becomes a peak value.
In such an automatic focusing device, generally, an area in an imaging area of the imaging device, which is used for determining the focus evaluation value and which is called an automatic focusing (AF) area, is located in the center part of the imaging area and has a predetermined fixed size.
The above-described focusing device has a deficiency in that an image which a photographer desires to photograph necessarily may not be in focus, if the AF area is large. For example, when a plurality of images which are located at different respective distances are photographed, the image which the photographer desires to focus typically may not be focused. Also, when the background of an image to be photographed is high in contrast relative to the image, the background of the image is focused depending upon, for example, a ratio between the image and the background in the AF area.
On the other hand, if the AF area is made small, even if an image located in the center of the AF area is intended to be focused, the image easily moves out of the AF area when the camera is moved or if the image itself slightly moves, which results in inaccurate focusing.
Accordingly, it is an object of the present invention to provide a novel and improved automatic focusing device for a digital camera that is capable of accurately focusing even when an image to be photographed is dark or low in contrast.
The above and other objects are achieved according to the present invention by providing a new and improved method, system and computer readable medium for controlling an automatic focusing device of a digital camera including receiving a light flux from an object to be photographed, the received light flux being passed through an optical system having a focusing lens system to form an image of the object and converting the received light flux into an output image signal; converting the image signal to output digital image data; outputting luminance data according to the digital image data as an automatic exposure (AE) evaluation value; setting at least an area of an imaging screen of an imaging device as an automatic focusing (AF) area; determining if the AE evaluation value is smaller than a predetermined value and setting an enlarged AF area as the AF area when the AE evaluation value is smaller than the predetermined value; integrating high frequency components of luminance data of image data in the AF area and outputting resulting data as an AF evaluation value; sampling AF evaluation values while moving the focusing lens system; and determining if the device is in focus based upon a result of the sampled AF evaluation values and driving the focusing lens system to a focusing position when the device is not in focus.
Another embodiment includes a method, system and computer readable medium for controlling an automatic focusing device of a digital camera including receiving a light flux from an object to be photographed, the received light flux being passed through an optical system having a focusing lens system to form an image of the object and converting the received light flux into an output image signal; converting the image signal to output digital image data; outputting luminance data according to the digital image data as an automatic exposure (AE) evaluation value; setting at least an area of an imaging screen of an imaging device as an automatic focusing (AF) area; integrating high frequency components of luminance data of image data in the AF area and outputting resulting data as an AF evaluation value; sampling AF evaluation values while moving the focusing lens system; and determining if the device is in focus based upon a result of the sampled AF evaluation values and driving the focusing lens system to a focusing position when the device is not in focus; and setting an enlarged AF area as the AF area before sampling the AF evaluation values when the AF evaluation value is smaller than a predetermined value.
Another embodiment includes a method, system and computer readable medium for controlling an automatic focusing device of a digital camera including receiving a light flux from an object to be photographed, the received light flux being passed through an optical system having a focusing lens system to form an image of the object and converting the received light flux into an output image signal; amplifying the image signal with a variable gain; converting the image signal to output digital image data; outputting luminance data according to the digital image data as an automatic exposure (AE) evaluation value; integrating high frequency components of luminance data of image data in an automatic focusing (AF) area and outputting resulting data as an AF evaluation value; sampling AF evaluation values while moving the focusing lens system; determining if the device is in focus based upon a result of the sampled AF evaluation values and driving the focusing lens system to a focusing position when the device is not in focus; and controlling the variable gain to increase the variable while sampling the AF evaluation values and when the AE evaluation value is smaller than a predetermined value.
Another embodiment includes a method, system and computer readable medium for controlling an automatic focusing device of a digital camera including receiving a light flux from an object to be photographed, the received light flux being passed through an optical system having a focusing lens system to form an image of the object and converting the received light flux into an output image signal; amplifying the image signal with a variable gain; converting the image signal to output digital image data; outputting luminance data according to the digital image data as an automatic exposure (AE) evaluation value; integrating high frequency components of luminance data of image data in an automatic focusing (AF) area and outputting resulting data as an AF evaluation value; sampling AF evaluation values while moving the focusing lens system; determining if the device is in focus based upon a result of the sampled AF evaluation values and driving the focusing lens system to a focusing position when the device is not in focus; and controlling the variable gain to increase the variable while sampling the AF evaluation values, when the AF evaluation value is smaller than a predetermined value before the sampling the AF evaluation values.
Another embodiment includes a method, system and computer readable medium for controlling an automatic focusing device of a digital camera including receiving a light flux from an object to be photographed, the received light flux being passed through an optical system having a focusing lens system to form an image of the object and converting the received light flux into an output image signal; converting the image signal to output digital image data; outputting luminance data according to the digital image data as an automatic exposure (AE) evaluation value; integrating high frequency components of luminance data of image data in an automatic focusing (AF) area and outputting resulting data as an AF evaluation value; sampling AF evaluation values while moving the focusing lens system; determining if the device is in focus based upon a result of the sampled AF evaluation values and driving the focusing lens system to a focusing position when the device is not in focus; controlling an AE control operation in accordance with the AE evaluation value; setting the AE evaluation value for the AF area independently from the AE control operation; and executing an AF operation after the AE operation for the AF area.